Electric batteries are commonly used to store and deliver electrical energy. One type of electric battery, known as a lead-acid battery, is commonly employed in vehicles (e.g. cars, trucks, boats, aircraft, and the like) for ignition, lighting, and other related purposes. These applications are typically known as "SLI" or "starting-lighting-ignition" functions.
A conventional lead-acid battery typically includes a number of electrochemical cells housed within a single battery housing. The electrochemical cells within a lead-acid battery are typically electrically connected in a series relationship such that the voltage supplied by the overall battery will be equal to the sum of individual voltages supplied by each electrochemical cell. In a typical application, for example, six two-volt electrochemical cells may be electrically connected within the housing of a single battery such that the battery supplies electrical energy at a voltage of twelve volts.
Each electrochemical cell in a lead-acid battery typically includes electrically-conductive positive and negative current collectors typically manufactured in the form of foraminous (porous) metallic grids. The individual current collectors may be planar (flat) in configuration or spirally-wound as discussed further below. Lead-acid electrochemical cells further include a supply of electrolyte solution therein. This electrolyte solution may be used in different ways within a given electrochemical cell. For example, the electrolyte may be present in liquid form wherein the electrolyte is not contained or absorbed in any structures. This type of battery is normally characterized as a "flooded battery" or "free electrolyte battery." Flooded batteries are generally constructed from planar (flat) positive and negative plates which are arranged in a parallel configuration having the electrolyte solution therebetween.
In contrast, another type of electrochemical cell which is conventionally known as a "retained electrolyte battery" involves a system in which the electrolyte solution is absorbed and retained within a separator element positioned between the plates. Retained electrolyte batteries may involve plate structures which are planar (flat) in configuration and arranged in a parallel orientation having the electrolyte-containing separator member positioned therebetween. Representative electrochemical cells of this type are discussed in the following U.S. Pat. No. 4,421,832 of Uba for ELECTROCHEMICAL CELL and U.S. Pat. No. 5,120,620 of Nelson et al. for BINARY LEAD-TIN ALLOY SUBSTRATE FOR LEAD-ACID ELECTROCHEMICAL CELLS, both of which are hereby specifically incorporated by reference for all that is disclosed therein.
In addition, retained electrolyte batteries may also be produced in a spirally wound configuration in which the positive and negative plates are wound together with the electrolyte-containing separator element positioned therebetween. Examples of this particular battery type are presented in the following U.S. patents: U.S. Pat. No. 4,064,725 of Hug et al for APPARATUS FOR MAKING SPIRALLY WOUND ELECTROCHEMICAL CELLS; U.S. Pat. No. 4,212,179 of Juergens for DRIVEN MANDREL AND METHOD; U.S. Pat. No. 4,346,151 of Uba et al. for MULTICELL SEALED RECHARGEABLE BATTERY; U.S. Pat. No. 4,383,011 of McClelland et al. for MULTICELL RECOMBINING LEAD-ACID BATTERY; U.S. Pat. No. 4,606,982 of Nelson et al. for SEALED LEAD-ACID CELL AND METHOD; U.S. Pat. No. 4,637,966 of Uba et al for SEALED LEAD-ACID CELL; U.S. Pat. No. 4,648,177 of Uba et al. for METHOD FOR PRODUCING A SEALED LEAD-ACID CELL; U.S. Pat. No. 4,780,379 of Puester for MULTICELL RECOMBINANT LEAD-ACID BATTERY WITH VIBRATION RESISTANT INTERCELL CONNECTOR; U.S. Pat. No. 5,091,273 of Hug et al. for METHOD OF APPLYING A TAIL WRAP TO A WOUND ELECTROCHEMICAL CELL AND CELL PRODUCED BY THE METHOD U.S. Pat. No. 5,871,862 of Olson for IMPROVED BATTERY PASTE COMPOSITIONS AND ELECTROCHEMICAL CELLS FOR USE THEREWITH and in U.S. patent application Ser. No. 08/888,905 filed Jul. 7, 1997 for BATTERY INTERNAL TEMPERATURE MEASUREMENT APPARATUS AND METHOD of Thomas J. Casale and Larry K. W. Ching, which are all hereby specifically incorporated by reference for all that is disclosed therein. Spirally wound batteries offer a high degree of efficiency and capacity in a minimal amount of physical space.
Lead-acid batteries may also be produced in two additional types, namely, (1) sealed; and (2) unsealed. In an unsealed battery, the interior of the battery housing is open to the ambient (outside) environment such that fluid communication exists between the interior and the exterior of the battery housing. Thus, in an unsealed battery, hydrogen and oxygen gases, which are produced by all lead-acid batteries during charging, are allowed to escape from the battery housing into the surrounding atmosphere.
Sealed batteries are also known as "recombinant" or "starved electrolyte" batteries. In this type of battery, the battery housing is substantially sealed to prevent the egress of gases therefrom during normal operating situations. In a sealed lead-acid battery, hydrogen and oxygen generated by the battery are retained within the battery housing and allowed to recombine into water molecules. A representative sealed (recombinant) battery system is discussed, for example, in U.S. Pat. No. 4,383,011, previously referenced.
Although referred to as a "sealed" battery, this type of battery typically includes a vent opening in the battery housing in order to relieve over-pressurization within the housing which may occur, for example, when the battery is abusively overcharged. The vent opening is typically in fluid communication with all of the cells of the battery such that gas generated by any of the cells may be vented. The vent opening is generally provided with a resealable safety valve which serves to release internal gas pressure above a predetermined superatmospheric pressure. The safety valve typically also functions as a check valve allowing gas flow in only one direction (i.e. out of the battery housing). A type of safety valve which is commonly used in sealed batteries for the above purposes is known as a "Bunsen" valve. A typical Bunsen valve may be designed to allow gas flow out of the battery housing only when the pressure differential between the housing interior and the ambient atmosphere reaches, for example, about 10 psi. Examples of batteries incorporating such safety valves are described in U.S. Pat. Nos. 4,346,151; 4,383,011; 4,421,832; 4,637,966 and 4,648,177, all previously referenced.
Gases produced by batteries, as described above, may create dangerous conditions under certain circumstances. As is well known, hydrogen gas, for example, is extremely flammable and may present an explosion risk if allowed to accumulate to a high enough concentration. In most single battery applications, the most significant risk posed by such hydrogen gas accumulation is that a spark near the battery will ignite the gas which has accumulated outside of the battery housing. The resulting flame may, in some cases, then propagate into the battery housing and ignite the hydrogen gas contained therein. This ignition of the gases within the housing may cause the battery housing to rupture and some of the acid contained within the battery housing to be ejected therefrom.
To counter this risk, most modern batteries are provided with flame arresters. Such flame arresters may be formed of a porous material which allows the passage of gas, but prevents flame propagation therethrough. In a sealed battery, for example, such a flame arrester may be located adjacent the safety valve.
Although the use of flame arresters generally prevents battery explosions, as described above, dangerous levels of gases, e.g., hydrogen gas, may still accumulate on the outside of battery housings in some situations. This problem of gas accumulation is heightened in multiple battery applications, e.g., applications where several batteries are located in close proximity to one another. One example of such a multiple battery application is a battery powered vehicle in which a cluster of batteries may be provided in a battery compartment. In multiple battery applications, due to the large number of batteries located in a relatively small and, sometimes, confined area, battery gases may accumulate to dangerous levels. Escaping battery gases also may carry electrolyte and/or acid out of the battery container and into the surrounding environment in the form of aerosol-like droplets. Such electrolyte and/or acid may cause damage to items with which it comes into contact.
Accordingly, even when batteries having flame arresters are used, it is desirable to provide venting of the individual batteries away from the battery compartment area in multiple battery applications.